G-SYNC 101: G-SYNC vs. V-SYNC OFF w/FPS Limit

At the Mercy of the Scanout

Now that the FPS limit required for G-SYNC to avoid V-SYNC-level input lag has been established, how does G-SYNC + V-SYNC and G-SYNC + V-SYNC “Off” compare to V-SYNC OFF at the same framerate?

The results show a consistent difference between the three methods across most refresh rates (240Hz is nearly equalized in any scenario), with V-SYNC OFF (G-SYNC + V-SYNC “Off,” to a lesser degree) appearing to have a slight edge over G-SYNC + V-SYNC. Why? The answer is tearing…

With any vertical synchronization method, the delivery speed of a single, tear-free frame (barring unrelated frame delay caused by many other factors) is ultimately limited by the scanout. As mentioned in G-SYNC 101: Range, The “scanout” is the total time it takes a single frame to be physically drawn, pixel by pixel, left to right, top to bottom on-screen.

With a fixed refresh rate display, both the refresh rate and scanout remain fixed at their maximum, regardless of framerate. With G-SYNC, the refresh rate is matched to the framerate, and while the scanout speed remains fixed, the refresh rate controls how many times the scanout is repeated per second (60 times at 60 FPS/60Hz, 45 times at 45 fps/45Hz, etc), along with the duration of the vertical blanking interval (the span between the previous and next frame scan), where G-SYNC calculates and performs all overdrive and synchronization adjustments from frame to frame.

The scanout speed itself, both on a fixed refresh rate and variable refresh rate display, is dictated by the current maximum refresh rate of the display:

As the diagram shows, the higher the refresh rate of the display, the faster the scanout speed becomes. This also explains why V-SYNC OFF’s input lag advantage, especially at the same framerate as G-SYNC, is reduced as the refresh rate increases; single frame delivery becomes faster, and V-SYNC OFF has less of an opportunity to defeat the scanout.

V-SYNC OFF can defeat the scanout by starting the scan of the next frame(s) within the previous frame’s scanout anywhere on screen, and at any given time:

This results in simultaneous delivery of more than one frame scan in a single scanout (tearing), but also a reduction in input lag; the amount of which is dictated by the positioning and number of tearline(s), which is further dictated by the refresh rate/sustained framerate ratio (more on this later).

As noted in G-SYNC 101: Range, G-SYNC + VSYNC “Off” (a.k.a. Adaptive G-SYNC) can have a slight input lag reduction over G-SYNC + V-SYNC as well, since it will opt for tearing instead of aligning the next frame scan to the next scanout when sudden frametime variances occur.

To eliminate tearing, G-SYNC + VSYNC is limited to completing a single frame scan per scanout, and it must follow the scanout from top to bottom, without exception. On paper, this can give the impression that G-SYNC + V-SYNC has an increase in latency over the other two methods. However, the delivery of a single, complete frame with G-SYNC + V-SYNC is actually the lowest possible, or neutral speed, and the advantage seen with V-SYNC OFF is the negative reduction in delivery speed, due to its ability to defeat the scanout.

Bottom-line, within its range, G-SYNC + V-SYNC delivers single, tear-free frames to the display the fastest the scanout allows; any faster, and tearing would be introduced.

Should “Reduce Buffering” option in Overwatch be enabled or disabled? Many competitive/pro players suggest having reduce buffering on to get higher framerate and reduced input lag but would having this option on have a negative effect on G-SYNC?

Also I recently upgraded my system to a i7-8700k and 1080ti. I usually sit at a steady 300fps on Overwatch now and use a 240hz monitor (Asus PG258Q). Would G-SYNC be worth using in this case?

“Reduced Buffering” is effectively Overwatch’s version of Nvidia’s “Maximum pre-rendered frames” set to “1,” so yes, leave it enabled for the lowest input lag, and no, it does not interfere with G-SYNC functionality; it was enabled for all the tests in this article. As for 240Hz G-SYNC w/238 or 237 FPS limit vs. 240Hz V-SYNC OFF w/238 or 237 FPS limit, the lag difference is almost zero; see the 240Hz chart on this page here. And for 240Hz G-SYNC w/238 or 237 FPS limit vs. 240Hz V-SYNC OFF at 300 FPS, you’re only looking at a 1ms difference in lag,… Read more »

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5 months 18 days ago

Member

pervyjutsu

So I’ve been experimenting with the different kinds of settings: – 240Hz G-SYNC w/ 238 or 237 FPS limit – 240Hz V-SYNC OFF w/ 238 or 237 FPS LIMIT – 240Hz V-SYNC OFF w/ 300 FPS limit I actually found myself liking 240Hz V-SYNC OFF w/ 238 or 237 FPS LIMIT the best. Up until now I have always used 300 FPS limit because that is what everyone said was best input lag-wise, but after trying the lower 238 or 237 limit today, wow I can aim so much better for some reason? It is definitely not placebo because I… Read more »

We always have to consider the (never to be underestimated) placebo effect, but… Like I mentioned in my last reply, the unique way each of those various scenarios deliver frames could be causing subtle differences in lag patterns that may affect aiming; muscle memory, conditioning, subconscious processes, etc. Because quite frankly, unless Overwatch is doing something abnormal with a 300 FPS limit above your refresh rate (which none of my existing tests show), or you’re experiencing a system specific issue, then the scenario you’re claiming feels more responsive, is actually slightly less responsive, at least where raw average input lag… Read more »

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5 months 17 days ago

Member

bcbuse

First, this is the best Gsync/Vsync information on the internet. I appreciate the effort you put into this, well done.

I read a comment you posted somewhere that ‘technically’ the absolute least input lag would be with Gsync Off + Vsync Off + Framerate upcapped(getting at least 2x the monitor refresh rate). Can you approximate how much less input lag that would be versus Gsync On + Vsync On(NVCP) + Framerate capped 2 below monitor refresh rate?

Depends on the maximum refresh rate and how high the framerate is sustained above it, but at 2x ratio, and at higher refresh rates, you’re looking at only 1-3ms less average input lag with G-SYNC off + V-SYNC off + FPS uncapped vs. G-SYNC on + V-SYNC on + -2 FPS limit when measured at crosshair level.

You can see the worst case first reaction differences between those two scenarios on the ninth page here.

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5 months 19 days ago

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daniel8747

to clarify: with fps capped 2-3 fps below monitor refresh rate, do i still need to have v-sync enabled?

Sort the comments here by newest; the answer is in the reply to the comment below yours, as well as in the “Range” section of this article.

Short answer to your question is “yes,” but only if you never want to see tearing.

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15 hours 36 minutes ago

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SturmButcher

I don’t understand something…. Why do I need V-Sync on with G-Sync?, The last one already sync frames and If I use a frame limiter I would never need V-Sync, I don’t understand guys. I am suspecting that G-Sync+V-Sync+RTSS is causing stutter in some games…Could you please enlighten me?

I’ve explained this ad nauseam (including in this article), but I’ll try to break it down as clearly as possible yet again… Within the G-SYNC range (e.g. within the refresh rate), G-SYNC is V-SYNC, and V-SYNC is G-SYNC. The “V-SYNC” option in the “on” position with G-SYNC enabled was originally a non-optional part of G-SYNC. It was only at a later point Nvidia revealed the V-SYNC “on/off” option in the control panel so that the screen would tear with V-SYNC “off” when the framerate exceeded the G-SYNC range/refresh rate, instead of reverting to V-SYNC behavior. However, the V-SYNC option also… Read more »

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16 days 4 hours ago

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vityapapa

The Csgo input-lagg is the best g-sync off+v-sync off and fps_max 0? i have 144hz monitor.